1. Field of the Invention
The present invention relates to optical fibers and transmission links for wavelength division multiplexing (WDM) systems, and more particularly to dispersion compensating optical fibers and transmission links including such fibers that have negative dispersions within an operating window and are particularly well suited for compensating dispersion of single mode fibers.
2. Technical Background
To meet the ongoing drive for more bandwidth at lower costs, telecommunications system designers are turning to high channel count dense wavelength division multiplexing (DWDM) architectures, longer reach systems and higher transmission bit rates. This evolution makes chromatic dispersion management critical to system performance, as system designers now desire the ability to accurately compensate dispersion across entire channel plans. Today, the only viable broadband commercial technology to battle dispersion has been Dispersion Compensating Modules (DCMs), i.e., spools having a suitable length of Dispersion Compensating Fiber (DCF) wound thereon. As DWDM deployments increase to 16, 32, 40 and more channels, broadband dispersion compensating products are even more desirable. Many current telecommunications systems have Single Mode Fibers (SMFs) that, although they are optimized for zero dispersion at about 1310 nm, can also be utilized effectively to transmit signals at wavelengths around 1550 nm. This enables erbium-doped fiber amplifiers to be employed. An example of such a SMF is SMF-28® manufactured by Corning Incorporated. Prior Art FIG. 2 illustrates the refractive index profile for such a SMF. Typically, such fibers are referred to as standard single mode fibers or step index single mode fibers and exhibit a dispersion of about 17 ps/nm/km and a dispersion slope of about 0.058 ps/nm2/km at 1550 nm.
With continuing interest in higher bit rate systems (>10 Gbs), broadband, long reach systems (e.g., >500 km) and optical networking, it is imperative to use DCFs in networks that carry data on SMF as well. High bit rates, longer reaches and wider bandwidths require dispersion to be compensated for more exactly.
Consequently, it is desirable for the DCF to have dispersion characteristics such that its dispersion is matched to that of the SMF transmission fiber it is required to compensate at the wavelength window of interest. The ratio of dispersion to dispersion slope at a given wavelength is referred to as “kappa (κ).” Kappa changes as a function of wavelength for a given transmission fiber. Hence, it is equally important that the kappa value of the DCF is closely matched to that of the transmission fiber in the operating window.
It would be desirable to develop alternative DCFs, in particular, ones having the ability to compensate for dispersion of SMF over a wide wavelength band around 1575 nm, and in particular over the C and L bands (from about 1525 to 1625 nm).